Vertical Cavity Surface Emitting Laser
Gideon Analytical Laboratories received several VCSELs (vertical cavity surface emitting laser" with diminished light capacity over time for failure analysis. VCSELs are a type of semiconductor laser diode with laser beam emission perpendicular from the chip surface. The VCSEL has become of great importance in the optical communications field. Gideon Analytical Laboratories was tasked to diagnose the failing VCSELs.
Failure analysis commenced. The devices were tested on a curve tracer to determine whether any junction problems (junction inversion, leakage current, facet oxidation, etc.) were present; there was no leakage current detected by the curve tracer. The VCSELs were then enclosed in a hermetic T0-46 can with a slanted anti-reflective glass coating radiating in the region of 795 nanometers, which is pictured below.
The glass window was inspected and was found to have deposits on the outside. Contamination was found on the glass window, and SEM-EDS analysis was performed; there were a high carbon and high sodium count. A micrograph of the contamination is pictured below. These contaminants may have attenuated the beam intensity when it traversed the glass window.
Failure analysis continued. The gold ball bond is connected to the laser via a gold trace in line which makes contact to the upper Bragg P-type reflector. The circumference of the circle was scanned using SEM-EDS to determine whether this area had undergone any changes. The micrograph is below, the red arrow points to the laser aperture. EDS analysis revealed no abnormalities in the laser aperture nor in the circumference surrounding the laser aperture.
Gideon Analytical Laboratories found no evidence of corrosion, facet oxidation, junction inversion, leakage current, or ESD damage. A more reasonable cause for these failures was the absorption of hydrogen on the aperture. This was consistent with all the evidence not found, the elements present and the residual gas analysis. This would have diminished the light intensity over time.
Gideon Analytical Laboratories helped dozens of companies in the electronics industry overcome problems in design, manufacture, or in the field. Companies can save time and money by contacting Gideon Analytical Laboratories and having failure analysis or analytical work performed. Companies can rest assured and receive peace of mind that they know the causes of failures and how to fix them.
TO-46 VCSEL package
VCSEL die ready for EDS analysis
Contaminated VCSEL window
Window contamination